1. Technical Field
The present invention relates to an integrated lead suspension that supports a magnetic head gimbal section of a hard disk drive, and more particularly to an integrated lead suspension that can improve problems that arise when a lead wiring pad provided on a flexure section of the suspension and a bonding pad provided on a slider of a head gimbal section of the suspension are joined.
2. Description of the Related Art
As hard disk drives have become smaller in recent years, the design and construction of the various parts of the suspension that moves the magnetic head have become more difficult, and, in particular, the task of connecting leads to the slider that holds the magnetic head has become extremely difficult. Moreover, the weight, wiring positions, and so forth, of the leads themselves have come to affect head control, and consequently integrated lead suspensions have come to be known in which variations due to wiring are suppressed by bonding a wiring section, or forming a wiring pattern, on the suspension.
With an integrated lead suspension, it is necessary to join together a lead wiring pad provided on the flexure section on the suspension side and a bonding pad provided on the slider, but the two connecting surfaces have a positional relationship such that the extended planes of the two pads are orthogonal (when the two planes are viewed from the side, a virtual right angle is formed at the point of intersection), and therefore the technology for connecting normal opposing planes cannot handle this case, and various new technologies are used.
For example, one known method for joining a lead wiring pad and bonding pad that have an orthogonal positional relationship is apple bonding, using a gold (Au) ball. With apple bonding, a gold ball is pushed into the virtual right angle formed by the above-described two pads, and connection is made by means of ultrasonic welding. An example of another method is a method using a solder ball for which application has been made by the present applicants in Japanese Patent Application No. 2000-189148 or Japanese Patent Application No. 2001-039888.
With a method using a solder ball, the integrated lead suspension is supported so that the virtual right angle formed by the above-described two pads faces upward vertically, and a solder ball is placed between the two pads. Following this, the solder is melted by irradiating the solder ball with a laser beam, connecting the two pads.
FIG. 15 is a drawing showing the case where the lead wiring pad and bonding pad are joined using a solder ball in a conventional integrated lead suspension. A suspension flexure 5 has a 2-layer construction comprising a polyimide layer 17, which is insulating polymeric material, and a stainless steel foil layer 18. A lead 10, which is a conductive layer, is further formed on the polyimide layer 17, and at the end of the lead 10 is formed a lead wiring pad 12 that is wider than the lead 10 so as to be of sufficient area for solder connection.
The shape of the polyimide layer 17 and stainless steel foil layer 18 can be processed by performing etching, for example, after coating the necessary parts with a resist. Also, when the polyimide layer 17 is a photosensitive polyimide layer, the shape can be processed by performing exposure and development after coating the necessary parts of the polyimide layer 17 with a resist or the like.
An aperture section 11 is formed in the tip section of the lead wiring pad 12 on the flexure 5 in order to prevent such problems as overflow of adhesive adhering to the lead wiring pad 12 when the slider is bonded to the suspension, or the polymeric polyimide layer 17 being altered by heat emission due to laser beam radiation. Therefore, the tip section of the lead wiring pad 12 comprises in-air wiring that projects into the aperture section 11.
A slider 6 that incorporates a magnetic head for a hard disk is attached to the flexure 5, and a bonding pad 15 of the slider 6 is placed in a position orthogonal to the lead wiring pad 12 as described above. Thus, the virtual orthogonal axes at which the plane extended from the plane of the bonding pad 15 intersects the plane extended from the plane of the lead wiring pad 12 form an angle of 90 degrees (a right angle).
When the bonding pad 15 and lead wiring pad 12 are connected with a solder ball, the suspension (flexure 5) is fixed in the direction in which the virtual right angle formed by the bonding pad 15 and lead wiring pad 12 opens upward in a vertical direction. Normally, the flexure 5 is fixed so that the lead wiring pad 12 on the flexure 5 and the bonding pad 15 on the slider 6 both form an angle 45 degrees above the horizontal while both maintaining a state in which the positional relationship of the two is orthogonal. Then a solder ball 400 is dropped from a solder ball transfer apparatus (not shown) between the two fixed pads. The two pads are then connected by melting the solder ball 400 by heating it by means of a laser beam radiation apparatus or the like (not shown).
With a conventional integrated lead suspension, the bonding pad 15 and lead wiring pad 12 are connected by means of a solder ball in this way. Integral-type wiring suspensions are classified into the three types below according to differences in their construction methods. In the construction of all three types, connection is performed as described above when the bonding pad 15 and lead wiring pad 12 are connected by means of a solder ball.
(a) An additive type in which copper foil wiring and pads are additively formed on insulating material of the suspension
(b) A subtractive type in which wiring and pads are formed by being etched from copper foil formed as a sheet on insulating material of the suspension
(c) An FPC type in which a flexible substrate (FPC) on which copper foil wiring and pads are formed is bonded to the suspension
However, with a conventional integrated lead suspension, when the bonding pad 15 and lead wiring pad 12 are connected by means of a solder ball there is problem in that, since the solder ball is almost spherical and the surfaces of the bonding pad 15 and lead wiring pad 12 are almost flat, the solder ball rolls in the virtual right-angle axis direction (direction A or direction B in FIG. 15) at which the extended planes of the two pads are orthogonal, and the position of the solder ball is displaced from the center line CL of each pad shown in FIG. 15. This problem arises in a similar way with all the above-described types.
Also, with the additive type, in particular, die wear occurs whereby areas near the edge take on an inclined beveled shape as shown in 12a through 12c in FIG. 15, as a result of which the area of the flat section 12d diminishes, and moreover, the surface of remaining flat section 12d is rough and has undulations. Consequently, the additive type is more susceptible than the other types to the problem of displacement of the position of the solder ball from the center line CL.
If the position of the solder ball is displaced from the center line, when the two pads are connected by melting the solder ball with laser beam radiation, there arises a solderless state in which there is no solder ball in the connecting region, or a solder connection defect because the solder ball, although in the connecting region, is displaced from the center line. Solder connection defects may include, in the case where solder does not connect both pads, partial soldering in which only parts of the two pads are imperfectly soldered, or a bridge connection that connects adjacent pads of the same kind.
The present invention has been devised in order to solve such conventional problems as described above, and has as its object the provision of an integrated lead suspension whereby, when a bonding pad and lead wiring pad are connected by means of a solder ball, the position of the solder ball is not displaced from the center line.